Assessment of the initial and aged dentin bond strength of universal adhesives

This study evaluated the effect of mechanical loading on microtensile bond strengths (μTBS) of universal adhesives to dentin and quantified adhesive dentin penetration using micro-Raman spectroscopy. Human molars had occlusal dentin exposed and were allocated into eight groups: All-Bond Universal and Scotchbond Universal using etch-and-rinse and self-etch approaches, Adper Prompt L-Pop, Adper Single Bond Plus, Clearfil SE Bond, and Optibond FL. Following bonding procedures and build-ups, specimens were either stored in water at 37 °C for 24 h or mechanically loaded (50,000 cycles, 50 N) prior to μTBS test. Additional teeth were prepared for micro-Raman analysis of adhesive penetration and FE-SEM. Data were analyzed by two-way ANOVA and Tukey׳s post hoc test (P<0.05). Mechanical loading had no deleterious effect on μTBS with the exception of Adper Prompt L-Pop. Incomplete infiltration of the demineralized dentin was noticed for adhesives using the etch-and-rinse approach and for Scotchbond Universal in the self-etch approach.     

Effect of proanthocyanidin incorporation into dental adhesive on durability of resin–dentin bond

BackgroundProanthocyanidin has shown to have beneficial effects on dentin bonding via its collagen cross-linking and protease inhibitory effects.ObjectiveThis study evaluated the effect of incorporation of 1–3% PA into a dental adhesive on durability of resin–dentin bond.Materials and methodsThe experimental adhesive was first formulated by combining 50 wt% comonomer mixtures with 50 wt% ethanol. PA was then added to the ethanol-solvated adhesive to yield three groups of adhesives at concentrations of 1.0 wt%, 2.0 wt% and 3.0 wt%. The PA-free adhesive served as control. Flat dentin surfaces from forty extracted third molars were etched with 32% phosphoric acid and the specimens were randomly assigned to one of the four adhesive groups. Two layers of experimental adhesives were applied to etched dentin and light-cured for 20 s after solvent evaporation. Composite build-ups were performed using Filtek Z250 (3M ESPE). The bonded teeth were divided into three subgroups for different methods of storage: (1) 24 h indirect water exposure (IE), (2) 6 M IE and (3) 6 M direct water exposure (DE). After the designated period of water storage, the bonded teeth were sectioned into 0.9 mm×0.9 mm beams for bond strength testing. Bond strength data were evaluated by two-way ANOVA and Tukey׳s tests (α=0.05). Interfacial nanoleakage was examined using a field-emission scanning electron microscopy. Two-way ANOVA and Tukey׳s tests were used to examine the effects of PA concentration and water exposure on bond strength and percentage of nanoleakage (α=0.05).ResultsTwo-way ANOVA showed that the factors, water exposure and PA concentration had a significant effect on bond strength (p<0.001). Interaction between the two factors was also significant (p<0.001). Bond strength of all four adhesives decreased with PA concentrations and ageing. Type of water exposure had no effect on the bond strength of PA-incorporated adhesive; while direct water exposure significantly reduced the bond strength of PA-free adhesive. Conversely, the factors, water exposure and PA concentration showed a significant effect on nanoleakage percentage (p<0.001). Interaction between the two factors was not significant (p>0.05).ConclusionIncorporation of proanthocyanidin into a dental adhesive did not prevent resin–dentin bond degradation over time.     

Effects of simulated pulpal pressure,mechanical and thermocycling challenge on the microtensile bond strength of resin luting cements

This study aimed at comparing the microtensile bond strength (µTBS) of three simplified luting strategies after different aging processes. Sixty human molars were prepared to expose flat middle dentin surfaces which received the following luting procedures: (i) SB+ARC – two-step etch-and-rinse adhesive+conventional resin cement (Adper Singlebond 2+RelyX ARC, 3M-ESPE); (ii) S3+PAN – one-step self-etch adhesive+conventional resin cement (Clearfil S3+Panavia F2.0, Kuraray Medical); (iii) U200 – self-adhesive resin cement (RelyX U200,3M-ESPE). The specimens were finally restored by indirect resin composite procedures (Filtek Z100,3M-ESPE). The aging regimens were water storage at 37 °C for one week (control), one week of 20 cm H₂O simulated pulpal pressure (SPP), 200,000 mechanical loading (ML) cycles, or 5000 thermal cycles (TC). The µTBS data was analyzed by two-way ANOVA and Tukey's test (α=0.05). SB+ARC showed significantly higher µTBS for control and all aging processes (p<0.001). Nevertheless, TC had no effect on the bond strength of SB+ARC. No difference in µTBS was observed between S3+PAN and U200 after SPP (p=0.251), but significant lower values were found for U200 after ML (p=0.010) besides being superior in the control groups (p<0.001). For U200, all ageing regimens induced significant reductions in the bond strength (p<0.001) with a more pronounced negative effect after ML. S3+PAN showed significant lower bond strength (p=0.010) only after ML aging. Two-step etch-and-rinse adhesive associated with dual-curing conventional resin cement may present the highest overall µTBS. However, the use of S3 one-step self-etch adhesive along with conventional resin cements may provide the most stable luting performance under the tested aging strategy.     

Post-treatment with high-power lasers to improve bond strength of adhesive systems to bleached dentin

To assess the effect of Er:YAG and diode lasers on the shear bond strength (SBS) of adhesive systems to bovine dentin submitted to bleaching with a high concentration agent. One hundred and twenty bovine dentin fragments were used. Fragments were distributed into 12 groups (n = 10) considering the bleaching (present or not), surface post-treatment (untreated, Er:YAG laser or diode laser) and adhesive system (total-etching or self-etching). Specimens received two applications of 38% hydrogen peroxide. Er:YAG laser (2940 nm, 200 mJ, 4 Hz) and diode laser (980 nm, 1.5 W) were applied for 15 s on bleached dentin surface. Restoration was performed with resin using split matrix. Specimens were submitted to SBS test and data (MPa) were analyzed by ANOVA and Tukey’s test (α = 0.05). SBS of bleached specimens decreased in comparison with non-bleached (p < 0.05). The highest values were obtained for the post-treatment with Er:YAG laser (p < 0.05). Total-etching adhesive was superior to self-etching system (p < 0.05). The irradiation of bleached dentin with Er:YAG laser followed by the application of the total-etching adhesive had similar SBS to unbleached dentin with no post-treatment (control) (p > 0.05). Er:YAG laser post-treatment followed by the total-etching adhesive system improve the bond strength of restorative material to bleached dentin.     

Influence of desensitizing procedures on adhesion of resin cements to dentin

This study evaluated the effect of two desensitizer agents with different contents and Nd:YAG laser irradiation on the shear bond strength (SBS) of adhesive resin cements to dentin. New treatment options of Nd:YAG laser irradiation and tetracalcium phosphate-containing agent applications were compared with routinely used glutaraldehyde-containing agents. One hundred and twenty human, caries-free premolars were embedded in acrylic resin blocks 2 mm below the cementoenamel junction. Buccal surfaces of the teeth were ground to expose dentin. The specimens were randomly assigned into three different surface treatments (desensitizing agents, Nd:YAG laser) and the control, then into three different adhesive resin cement applications (n = 10). Resin cements (Panavia SA cement (PA), Panavia SA cement with Clearfil Universal Bond (PACU), and Multilink N (MN)) were applied to the conditioned teeth surfaces using Teflon tubes. The specimens were thermocycled (5000 cycles, 5–55 ± 1 °C, dwell time 30 s). The SBS test was performed in all groups. The results were submitted to two-way ANOVA and Tukey HSD tests (p < .05). Further, SEM analysis was performed on the dentin surfaces. SBS values were significantly difference among the surface treatment groups and also among adhesive resin cement groups (p < .05). The specimen cemented with PA showed lower SBS values than PACU- and MN-applied specimens. The highest SBS value was obtained in the Nd:YAG laser group which was cemented with PACU cement. The lowest SBS value was obtained in the control group which was cemented with PA cement. In addition, SEM evaluation revealed that desensitizing agents and Nd:YAG laser occluded dentin tubules.     

Influence of storage time on bond strength of self-etching adhesive systems to artificially demineralized dentin after a papain gel chemical–mechanical agent application

ObjectivesThe aim of this study was to evaluate the influence of storage time on the bond strength of self-etching adhesive systems to artificially demineralized dentin submitted to application of a papain-based chemical mechanical agent for carious tissue removal.Materials and MethodsTwenty-four blocks of human coronal dentin were randomly divided into 2 groups: (1) restored with a two-step self-etching adhesive system (Clearfil SE Bond); (2) restored with a one-step self-etching adhesive system (One-Up Bond F Plus). After artificial caries induction, the specimens were treated with papain-based gel, received an application of the adhesive system according to the respective group, and blocks of microhybrid resin composite measuring 5.0 mm high and 5.0 mm wide were fabricated incrementally on the tooth, which would later be cut to obtain sticks with a bond area of around 1 mm², for use in the microtensile tests. After this, half of the sticks obtained from each tooth were submitted to the microtensile test 24 h later, while the other half were stored in water, in an oven at 37° C for a period of 180 d. The specimens were submitted to the microtensile test in a Universal Test Machine at a speed of 0.5 mm/min. The surfaces of the fractured test specimens were examined visually under a stereoscopic loupe in order to classify the fracture type. After exploratory analysis of the data, the two-way Analysis of Variance (ANOVA) and the Tukey test were applied. The data on the fracture types were analyzed by the Exact Fisher test.ResultsNo statistically relevant differences were verified among the means of the microtensile bond strength values of the adhesive systems evaluated in the different storage times. Mixed and adhesive fractures types were observed for both groups.ConclusionStorage time did not influence the bond strength of the two-step or one-step self-etching adhesive systems to artificially demineralized dentin submitted to application of a papain-based chemical mechanical agent for carious tissue removal. Both adhesive systems provided similar bond strength at different storage times.     

Development of a simplified etch-and-rinse adhesive containing niobiophosphate bioactive glass

PurposeThe aim of this study was to evaluate radiopacity, degree of conversion (DC), Knoop hardness (KHN), ultimate tensile strength (UTS) and microtensile bond strength (µTBS) to dentin of an experimental adhesive containing micro-filler of niobium–phosphate bioactive glass (NPG).Materials and methodsThe NPG glass was produced by fusion of NbO₅, Na₂CO₃, CaO, (NH₄)₂HPO₄ at 1400 °C. After cooling, the glass was ground to a mean particle size<25 µm, and either added (40 wt%) to an experimental adhesive resin mix containing monomers and solvent, or not. The DC of the adhesives was evaluated by Fourier transform infrared spectroscopy. Flat dentin surfaces were obtained from 16 molar teeth, and prepared for use to evaluate µTBS (n=8). An hourglass-shaped matrix (UTS and KHN) or disk-shaped matrix (radiopacity) was filled with adhesive and light-polymerized. The data from each test were analyzed by appropriate statistical methods.ResultsThe presence of glass particles made the adhesive system radiopaque. Addition of bioactive NPG glass particles to the adhesive system prevented decreases in bond strength; reduced the UTS and increased DC and KHN. All groups showed predominance of adhesive failure mode.ConclusionAddition of 40% NPG glass may be an alternative to obtain an adhesive system with adequate mechanical and bond strength to dentin properties.     

Effect of an Er,Cr:YSGG laser preparation on dentin bond strength of a universal adhesive

The aim of this study was to evaluate the bond strength of a universal adhesive system to dentin prepared with SiC paper or an Er,Cr:YSGG laser using different bonding strategies (etch-and-rinse versus self-etch mode). Ninety-six extracted caries-free, sound human molars were used. The teeth were longitudinally sectioned in the mesiodistal direction and were wet polished with 600-grit SiC paper to obtain a standardized flat dentin surface. All prepared teeth were randomly divided into two groups, according to the surface preparation method: GroupI:an erbium, chromium:yttrium,scandium, gallium, garnet laser; Group II: silicon carbide paper[SiC] (n = 48). Each group was then assigned into three subgroups according to the universal adhesive’s (Single Bond Universal) bonding strategies: (a) etch-and-rinse mode with phosphoric acid, (b) etch-and-rinse mode with a laser, (c) self-etch mode (n = 16). For surface preparation, the Er,Cr:YSGG laser was used at 3 W, 30 Hz with 140 μs pulse duration for 25 s. For etching mode, the laser was used at 1.5 W (60% air, 70% water). Cylinders of composite were fabricated on the bonding area and shear bond strength was determined using a universal testing machine. Failure modes were evaluated using a stereomicroscope. The data were analyzed using two-way ANOVA followed by the Bonferroni test (p < 0.05). Bonding strategies showed statistically significant differences in both the SiC-and laser-prepared groups (p < 0.05).Universal adhesive used in etch-and-rinse mode with acid showed significantly higher bond strength values than in self-etch mode (p < 0.05). The bond strength values did not differ according to the surface preparation method (p > 0.05). Irrespective of preparation method, using universal adhesive in etch-and-rinse mode with acid might improve dentin bond strength. Laser preparation did not affect the bond strength of the universal adhesive tested.     

Pulsed laser heating process of multi-walled carbon nanotubes film

The prepared multi-walled carbon nanotubes (MWCNTs) film was mounted on the holder and the film surface was flashed with a single pulse of Nd:YAG laser (λ = 532 nm) in the air. The dynamics of pulsed nanosecond laser heating process was simulated by the solution of the one-dimensional heat conduction equation. The finite element method (FEM) was applied to solve the equation. At the laser fluence of 1 J/cm² with Nd:YAG laser, the surface reached the maximum temperature 1503 °C at 13 ns. Moreover, the Raman spectroscopy of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts I_D (defect-mode) and I_G (graphite-mode) was measured by the Raman spectroscopy. The maximum surface temperature was calculated and compared with the I_G/I_D ratio of MWCNTs film. The graphitization occurred on the sample after irradiation.     

Direct thermal diffusion bonding of Nd:YAG/YAG composite transparent ceramics by vacuum sintering

Nd:YAG/YAG transparent ceramics were prepared by vacuum sintering at 1780 °C for 40 h and annealed at 1450 °C for 20 h in air. Two separately polished Nd:YAG/YAG samples were bonded into monolithic and uniform composite-material followed by vacuum sintering at 1790 °C for 50 h under uniaxial pressure of 60 MPa, and then annealed at 1450 °C for 100 h in air. The fracture strength of bonded samples at the bonding interface is higher than that of as-prepared Nd:YAG/YAG samples. Meanwhile, the extinction coefficient of bonded samples is 0.0305 cm⁻¹ which is an improvement over as-prepared samples. The microstructure of the contact interface reveals the disappearance of the contact layer at the bond due to the grain growth and coalescence mainly based on grain boundary diffusion at higher temperatures and longer heat-treated time, which indicates that the bonding technology is beneficial to the fabrication of the thick composite materials.     

A novel silane system as a primer for orthodontic bonding—A pilot study

AimTo determine the adhesion strength (measured as shear bond strength, SBS) of orthodontic brackets using two experimental silane-based primer systems and compare and contrast their effect.Materials and methodsSixty acid-etched premolars were randomly assigned into 4 study groups (n=15). In group 1, brackets were bonded without primer but using Transbond XT adhesive; in group 2, Transbond XT primer was applied and bracket bonded; in group 3, an experimental silane-based primer of 1.0 vol% of 3-acryloxypropyltrimethoxysilane (ACPS) was applied before bonding; in group 4, an experimental silane-based primer of 1.0 vol% of ACPS+0.5% bis-1, 2-(triethoxysilyl) ethane (BTSE) was used. The adhesion strength (measured as shear bond strength) was recorded using a universal testing machine. Failure types were classified according to the Adhesive Remnant Index (ARI). Contact angles of the primers were measured on an enamel slab.Data was analyzed by ANOVA and Tukey's multiple comparison post hoc analysis.ResultsThe mean adhesion strength results were high in group 4: 15.8±1.6 MPa followed by group 3: 12.5±1.5 MPa, group 2: 11.9±1.1 MPa and the lowest in group 1: 08.1±0.7 MPa. A significant difference in adhesion strength was observed between all the groups except for group 3 and group 4 (p<0.01).The ARI score was distributed largely to 0 and 1. One instance of enamel fractures was recorded in group 1. The contact angle measurements suggested that the lowest value with the experimental primer containing (ACPS+BTSE) was, <5° followed by Transbond XT, 41.86±4.56°.ConclusionThe experimental silane primer systems were hydrophilic in nature and demonstrated higher adhesion strength compared to traditional orthodontic primers.     

Multilayer YAG/Re:YAG/YAG laser ceramic prepared by tape casting and vacuum sintering method

This paper reports the use of tape casting and vacuum sintering process for the fabrication of optical grade YAG/Re:YAG/YAG (Re = Yb or Nd) composite laser ceramic. The influence of dispersant content on the rheological behavior of the slurry, the microstructure, the optical and laser performances, were studied. The experimental results showed that laser output at 1030 nm was generated for YAG/Yb:YAG/YAG with threshold absorbed pump power of 4.33 W and slope efficiency of about 12% when the transmission of output coupler (T_oc) was 2.3%. For YAG/Nd:YAG/YAG ceramic, 1064 nm laser output was obtained, and the slope efficiency increased from 30% to 38% while T_oc changed from 2.3% to 10%.     

Incorporation of inorganic fillers into experimental resin adhesives: Effects on physical properties and bond strength to dentin

This study investigated the effect of different monomeric systems and inorganic fillers on the physical properties of experimental resin adhesives and on the immediate and 6-month bond strength to dentin. Two, 2-step self-etch adhesive systems were prepared: two primers (constituted of GDMA-P, ethanol, water, and HEMA or PEG(400)-UDMA) and two adhesives (constituted of Bis-GMA, TEGDMA, and HEMA or PEG(400)-UDMA). Next, the adhesives were allocated into three groups according to filler incorporated: unfilled (control), silica (SiO₂), or ytterbium trifluoride (YbF₃). Degree of conversion (DC, after 30 and 60 s of light-activation), water sorption (WS) and solubility (SL), and flexural strength (σ) and modulus (E_f) tests were performed for all adhesives. A microtensile bond strength (µTBS) test to dentin was evaluated after 24 h (immediate) and 6 months (6-month) of water storage using a universal testing machine (DL500, EMIC). Data were analyzed using statistical tests (α=5%). The adhesives showed similar DC at a same light exposure time, although light-activation for 60 s improved conversion of monomers. The unfilled HEMA-containing adhesive showed higher WS, SL, σ and E_f compared to others. The incorporation of fillers into the adhesives did not affect negatively the immediate µTBS results; however, after 6 months the presence of SiO₂ impaired in complete premature failures, and the presence of YbF₃ reduced the µTBS in the PEG(400)-UDMA-based group. The unfilled HEMA-containing group also reduced bond strength after 6 months of water storage. In conclusion, depending on the resin matrix composition, YbF₃ seems to be a good option for reinforcing adhesive systems.     

Strengths of additions to composite or resin-modified glass-ionomer

ObjectivesAdding a new layer of material to cured resin-based composite (RBC) or resin-modified glass ionomer (RMGI) restorations is necessary in dental practice. This study investigated strengths of additions to the two materials.Material and methodsBeam-shaped specimens were made from monolithic RBC or RMGI, or additions of RBC and RMGI onto RBC or RMGI half-bar substrates. For the additions, the substrates were left undisturbed or were ground with silicon carbide paper followed by the application of a self-etch adhesive. Sample size was 10. Flexural strengths were determined by a 4-point bending test in a universal testing machine. Results were statistically analyzed with one-way ANOVA followed by Student–Newman–Keuls post-hoc test (α=0.05).ResultsFlexural strength of the monolithic RBC (86.7±21.8 MPa) was significantly higher than RMGI (52.6±13.1 MPa). Addition of RBC to cured RBC significantly reduced flexural strength regardless of the substrate surface conditions (34.1±11.5–45.7±21.1 MPa). Addition of RMGI to cured RMGI did not significantly reduce flexural strength (36.2±8.4–52.7±25.2 MPa). Flexural strength of RBC added onto cured RMGI that was ground and bonded was the lowest (21.5±10.0 MPa). Most specimens from this group exhibited adhesive failure.ConclusionsRBC/RBC additions reduced flexural strength whereas flexural strength of RMGI/RMGI additions was not significantly lower than its cohesive strength. RBC added onto RMGI in the sandwich restorative configuration had lowest failure strength.     

Bond strength and adhesive interface analysis using EDTA as a dentin conditioner

This study evaluated dentin bond strength and dentin-resin interfacial morphology using phosphoric acid-etching and EDTA-conditioning. The occlusal enamel of twenty-four human third molars was removed to expose the dentin surfaces, which were polished with a SiC paper (600 grit). Teeth were randomly divided into three groups (n = 8): etching with 37% phosphoric acid (15 s), conditioning with 0.1 M EDTA (60 s) and 0.5 M EDTA (120 s). Adhesive (XP Bond, Dentsply) was applied and three layers (2 mm each) of composite (EsthetX, Dentsply) were placed and light-activated separately (20 s). Teeth were sectioned to obtain specimens for the microtensile bond strength test (1 mm² at cross section). Half of the specimens was tested in a universal testing machine (EZ Test, Shimadzu) after 24 h and the other half after storage for 10 months. Failure mode and adhesive interface were analyzed using scanning electron microscopy. Data were analyzed by mixed models for repeated measures (PROC MIXED) and Tukey-Kramer test, considering a significance level of 5%. Mean bond strength values (SD) after 24 h and 10 months were, respectively (in MPa): phosphoric acid: 37.3 (7.7) / 33.9 (6.7); 0.1 M EDTA: 14.7 (7.3) / 15.1 (10.1); 0.5 M EDTA: 25.1 (7.7) / 21.1 (14.1). Dentin treatment with EDTA and phosphoric acid resulted in hybrid layer and resin tags formation. Mixed failures were prevalent for all groups tested after 24 h. Storage for 10 months changed the failure mode for the 0.5 M EDTA group to adhesive failure (between dentin and bonding agent). EDTA applied for 60 s yielded lower bond strength results compared to phosphoric acid and EDTA (120 s), but there was no significant reduction after 10 months of storage for any of the tested groups.     

Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO₂) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τ_FWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO₂/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO₂ NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.     

Effect of epigallocatechin gallate,green tea extract and chlorhexidine application on long-term bond strength of self-etch adhesive to dentin

This study evaluated the effect of dentin pretreatment with metalloproteinase inhibitors on long-term microtensile bond strength (μTBS) of self-etch adhesive (SEA) to dentin. Thirty-two dentin fragments received pretreatments (n=8): C: control (not treated); GT: 2% green tea extract; CLX: 2% chlorhexidine; EGCG: 2% epigallocatechin gallate. SEAs (Clearfil SE Bond) and resin composite were applied to dentin surface. After 24 h, resin-blocks were cut into sticks submitted to μTBS testing immediately or after 6 months of storage in water. Two-way ANOVA and Tukey test (α=5%) indicated that CLX group showed μTBS values statistically superior to the other groups at immediate testing, whereas those of EGCG group were the lowest (p=0.018). After 6 months, a significant increase in μTBS values was observed for all groups, except for CLX (p=0.018). In conclusion, μTBS increased in dentin pretreatment with EGCG and green tea groups, and in the non-treated group.     

Iodonium salt improves the dentin bonding performance in an experimental dental adhesive resin

The aim of this study was to evaluate the influence of an iodonium salt on the immediate and long-term microtensile bond strength to dentin of an experimental dental two-step, self-etching adhesive system. A model dental adhesive resin was formulated using bisphenol A glicidyl dimethacrylate (Bis-GMA), triethylene glicol dimethacrylate (TEGDMA), and hydroxyethyl methacrylate (HEMA), which was polymerized using four combinations of photo-initiators and coinitiators. A group using only camphorquinone (CQ), two binary systems (CQ and ethyl 4-dimethylamine benzoate (CQ+EDAB), CQ and diphenyliodonium hexafluorphosphate (CQ+DPIHFP)) and a ternary system (CQ+EDAB+DPIHFP) was investigated. Clearfil SE Bond (CSEB) was used as a commercial reference. Bond strength to bovine dentin was assessed through microtensile bond tests measured in MPa in a universal testing machine. The beam specimens were stored in distilled water at 37 °C for 24 h and 1 year. Two-way ANOVA and Student–Newman–Keuls' post-hoc tests were used to compare means of groups (α=5%) and failure modes classified under magnification. After 24 h, the ternary system showed a bond strength similar to that of the binary system CQ+EDAB and the commercial material. After 1 year of storage, the μTBS values of the group CQ+EDAB+DPIHFP showed a bond strength significantly higher (p<0.05) than those of the CQ, CQ+DPIHFP, and CQ+EDAB groups and no difference from that of the CSEB group. The ternary photo-initiator system with iodonium salt maintained increased bond strength to dentin of model self-etching adhesive systems after 1 year of aging.     

Bond strength and chemical interaction of self-adhesive resin cements according to the dentin region

The aim of the study is to evaluate the effectiveness and level of chemical interaction of self-adhesive resin cements (SRCs) according to the dentin region. One hundred eight sound human third molars and three SRCs were selected: Bifix SE (Voco), Maxcem Elite (Kerr), and RelyX U200 (3M ESPE). Ninety human molars were used for the bond strength test and 18 teeth for the X-ray diffraction (XRD) characterization. A flat surface of superficial, deep, or axial dentin was exposed. For bond strength evaluation, 90 indirect composite resin restorations (10 mm in diameter, 2.0 mm-thick) were built and cemented with one of the SRCs according to the manufacturer's instructions. The restored teeth were then cut into sticks with cross-sectional areas of 0.8 mm² and tested in tensile at a speed of 0.5 mm/min (n=10). The results of bond strength were statistically analyzed by two-way ANOVA and Tukey's test (α=0.05). The fractured specimens were classified under SEM. The remaining teeth were further sectioned in order to build dentin fragments with 2.0 mm² of area and 0.2 mm in thickness for XRD analysis. In general, significantly higher bond strength was found when bonding to axial and deep dentin compared to superficial dentin. Comparing the bonding effectiveness of the SRCs, taking into account the mean bond strength obtained in the 3 dentin regions, the study found no significant difference (p>0.05). Although RelyX U200 showed similar bond strength irrespective of the dentin region (p>0.05), the bonding results of the other 2 SRCs varied significantly (p<0.05). There was a higher incidence of cohesive failure in the SRCs for all groups. The XRD analysis detected different perceptual reductions of hydroxyapatite crystallinity for all SRCs, indicating a particular chemical interaction in each experimental condition. Thus, it can be concluded that the bond strength and chemical interaction of the SRCs can vary significantly according to the dentin region.     

Nanosecond-laser patterning of 3Y-TZP: Damage and microstructural changes

The aim of this study is to characterize in detail the microstructural changes and collateral damage induced by direct laser patterning on the surface of dental-grade zirconia (3Y-TZP) employing an interference setup with the 532 and 355 nm harmonics of a Nd:YAG laser (pulse duration of 10 ns).Laser-material interaction mainly results in thermal effects for both wavelengths studied. Upon laser irradiation the material locally melts producing pattern and establishing a steep thermal gradient on the surface. This generates a ∼ 1 μm thick heat affected zone where microcracking, directional recrystallization, phase transformation (from tetragonal to monoclinic, t → m) and texturization (ferroelastic domain switching) take place. In addition, surface coloration results from the activation of F-centers as a consequence of high energy radiation exposure. No chemical segregation or diffusion was detected. All these microstructural changes should be taken into account to ensure integrity and long-term reliability of the zirconia components.